Creating formatted output using picture strings

Olof Bjarnason olof.bjarnason at gmail.com
Wed Feb 10 13:46:31 CET 2010


2010/2/10 Alf P. Steinbach <alfps at start.no>:
> * Olof Bjarnason:
>>
>> 2010/2/10 Peter Otten <__peter__ at web.de>:
>>>
>>> python at bdurham.com wrote:
>>>
>>>> Does Python provide a way to format a string according to a
>>>> 'picture' format?
>>>>
>>>> For example, if I have a string '123456789' and want it formatted
>>>> like '(123)-45-(678)[9]', is there a module or function that will
>>>> allow me to do this or do I need to code this type of
>>>> transformation myself?
>>>
>>> A basic implementation without regular expressions:
>>>
>>>>>> def picture(s, pic, placeholder="@"):
>>>
>>> ...     parts = pic.split(placeholder)
>>> ...     result = [None]*(len(parts)+len(s))
>>> ...     result[::2] = parts
>>> ...     result[1::2] = s
>>> ...     return "".join(result)
>>> ...
>>>>>>
>>>>>> picture("123456789", "(@@@)-@@-(@@@)[@]")
>>>
>>> '(123)-45-(678)[9]'
>>>
>>> Peter
>>> --
>>> http://mail.python.org/mailman/listinfo/python-list
>>>
>>
>> Inspired by your answer here's another version:
>>
>>>>> def picture(s, pic):
>>
>> ...   if len(s)==0: return pic
>> ...   if pic[0]=='#': return s[0]+picture(s[1:], pic[1:])
>> ...   return pic[0]+picture(s, pic[1:])
>> ...
>>>>>
>>>>> picture("123456789", "(###)-##-(###)[#]")
>>
>> '(123)-45-(678)[9]'
>
> I learned a bit by Peter Otten's example; I would have gotten to that
> notation sooner or later, but that example made it 'sooner' :-).
>
> I think your version is cute.

Thanks!

Here's another version (maybe a little more readable?):

def first(s): return s[0]

def rest(s): return s[1:]

def picture(s, pic):
  if not s: return pic
  if first(pic)=='#': return first(s)+picture(rest(s), rest(pic))
  return first(pic)+picture(s, rest(pic))


>
> I'd probably write it in a non-recursive way, though, like
>
>    def picture( s, pic, placeholder = "@" ):
>        result = ""
>        char_iter = iter( s )
>        for c in pic:
>            result += c if c != placeholder else next( char_iter )
>        return result
>
> Of course this is mostly personal preference, but there is also a functional
> difference.
>
> With your version an IndexError will be raised if there are too /many/
> characters in s, while too few characters in s will yield "#" in the result.
>
> With my version a StopIteration will be raised if there are to /few/
> characters in s, while too many characters will just have the extraneous
> chars ignored.
>
>
> Cheers,
>
> - Alf
> --
> http://mail.python.org/mailman/listinfo/python-list
>



-- 
http://olofb.wordpress.com



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